From reading the filings in Walters v. Flint it appears to me that they hired an outside engineering firm to plan their switchover and that firm failed to warn

From reading the filings in Walters v. Flint it appears to me that they hired an outside engineering firm to plan their switchover and that firm failed to warn them of any urgent need for corrosion control. The outside engineering firm argues that they didn't warn flint because they assumed flint would be using corrosion control. When it became clear that there were serious water quality issues, flint hired another outside engineering firm to review and monitor their system and make recommendations and the second engineering firm failed to identify the lack of corrosion control as a safety issue. They basically said 'you could add phosphates to reduce complaints about discolored water, but you're still going to get lots of complaints about discolored water'. To me it seems like a lot of the root cause was that they knew and expected the river water source would have serious cosmetic issues, but they felt forced into it. When things started going wrong they kept treating it as cosmetic issues (and it sure sounds that by count most of the complaints they had were cosmetic issues) even though the water was actually unsafe. With two outside water engineering firms, on top of the city's own staff not catching this... I think the explanation has to be more complicated than someone being criminally negligent.